If you've ever visited /mu/ on 4chan you know it's generally just a bunch of people whining about indie or metal or some new album that came out. But occasionally there are the good sharethreads where people come together and share a lot of really good music, almost all with mediafire links so you can just download everything you think looks appealing. Organized by timeframe and the theme of the sharethread (electronic, metal, indie etc...)
http://killerplacebo.com/mu/